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Timing Is Critical to Vaccine Effectiveness

Establishing an effective vaccination protocol for Mycoplasmal pneumonia in young pigs is a balancing act. Pig performance and serology can help.Vaccinate pigs too young, when maternal antibody levels are too high, and the vaccine may not be very effective, explains David Bomgaars, swine practitioner at Orange City, IA. Wait too long to vaccinate and disease exposure may be too extensive.Bomgaars

Debra Neutkins | Nov 15, 2000

Establishing an effective vaccination protocol for Mycoplasmal pneumonia in young pigs is a balancing act. Pig performance and serology can help.

Vaccinate pigs too young, when maternal antibody levels are too high, and the vaccine may not be very effective, explains David Bomgaars, swine practitioner at Orange City, IA. Wait too long to vaccinate and disease exposure may be too extensive.

Bomgaars tries to stack the deck in his clients' favor by evaluating serology and pig performance before recommending a vaccination protocol for Mycoplasmal pneumonia.

Vaccination timing in young pigs depends on vaccination status and natural exposure in the sow.

"If maternal antibody level is too high, the vaccine may not give adequate protection," he explains. "We feel we get better protection when we give the vaccine when pigs are a little older. Often, maternal antibodies are at the lowest level when pigs are 10-12 weeks of age. But, we don't want to wait too long, either, or too much exposure can occur before we give the vaccine."

Once exposed to mycoplasma, pigs may take four to eight weeks to seroconvert. That means pigs can show clinical signs of mycoplasma in the finishing barn, but blood tests will come up negative.

There is a diagnostic alternative, however. The technique called "nested PCR" (polymerase chain reaction) samples nasal secretions and combines two tests to identify the specific DNA strand of mycoplasma. The test takes only about five hours to complete.

Mike Eisenmenger, DVM, Swine Vet Center, St. Peter, MN, participated with the University of Minnesota using nested PCR for on-farm mycoplasma validation. Serology, PCR and clinical signs were used in combination to determine when the organism was moving in the population.

The beauty of the technique is that it detects mycoplasma sooner than serology, and it's practical, says Eisenmenger.

"We're finding the PCRs come up positive several weeks prior to a serological response," he says. "PCR accurately predicts when mycoplasma is making its biggest move. If I'm trying to make a vaccination decision, PCR and serology combined provide good information. Before, we always had to assume a four-week interval between first exposure and immune response."

The only drawback to PCR becoming a useful on-farm diagnostic tool is the cost - about $35/sample tested.

"When you want to do 20 samples multiple times, the cost adds up," says Eisenmenger. "But when you're trying to make solid vaccination decisions for thousands of pigs, in the big scheme of things, it's not that expensive."

If PCR is positive and clinical signs are negative, does he assume infection? "Yes, but we don't use this as an individual animal test. It's a population test," explains Eisenmenger. "The PCR test helps determine the vaccination window. That's why we implemented it with serology. We graph pigs across time, serial bleeding every four weeks and look at when PCR spikes. We're making the assumption that spike is when transmission occurs. We want to vaccinate ahead of that by roughly four weeks."

Mycoplasma Hits at 18 Weeks Mycoplasma typically affects pigs at 20 weeks of age and older with coughing, uneven growth and death loss, says Eisenmenger. "We routinely diagnose mycoplasma, accompanied by porcine reproductive and respiratory syndrome (PRRS) and swine influenza virus (SIV). We base the decision to vaccinate on what is happening in the finisher. We also look at how (different) genetic lines perform in healthy barns compared to barns infected with mycoplasma, mycoplasma and PRRS, or mycoplasma, PRRS and SIV.

"Pigs posted between the 10th and 16th weeks have a few lesions, but not in an amount to cause the death loss and problems some herds experience," says the Minnesota veterinarian. "No doubt, deaths that do occur in PRDC (Porcine Respiratory Disease Complex) outbreaks are related to ulcers. This is a real problem in PRDC cases.

"We see nice big pigs `bleach out' and die rapidly when they go off feed from pneumonia or we get chronic anemic pigs that do poorly and end up at a cull market. It's very important to keep pigs on feed and to track death rate, culls and lights when deciding whether to vaccinate. Many respiratory problems are alleviated when we vaccinate for mycoplasma," Eisenmenger adds.

The sow farms serviced by the St. Peter, MN-based clinic commonly vaccinate for mycoplasma. Sows are vaccinated, prefarrowing, across all parities to "undo parity effects on transmission," Eisenmenger explains.

Some herds vaccinate for mycoplasma six weeks prefarrowing in an attempt to provide uniform levels of maternal antibodies to all piglets, whether farrowed by a gilt or a sixth-parity sow. Incoming gilts are also vaccinated.

One-Dose Vaccination A new mycoplasma vaccine with an Amphigen adjuvant offers one-dose vaccination, a convenient option, which makes proper timing a key consideration.

"If one dose is as efficacious as a two-dose vaccine, that's fantastic," says Pat Halbur, veterinary pathologist, Iowa State University Diagnostic Laboratory. "Labor is a huge issue in the pork industry. My concern is timing. If you only have one shot at them, you want to make sure the timing is right."

Serology is still the most practical tool to help get vaccination timing right, notes Halbur. But ideally, the combination of serology, PCR and necropsy results will best characterize the timing of disease exposure and progression of disease in different systems.

Halbur says diagnostic work has helped him identify which vaccination strategies don't work. "We see a lot of submissions from herds that have used (just) one dose of a two-dose vaccine (program). That strategy fails many, many times," he adds.

A new one-dose product, RespiSure-One (Pfizer Animal Health) provides flexibility for vaccination timing. Data from studies show the product significantly reduced mycoplasma-related lung lesions 23 weeks after challenge in pigs vaccinated either at 3 weeks of age or 8 weeks of age.

Eisenmenger says he'll likely use the vaccine in pigs 9 weeks of age. With a 23-week duration of immunity, pigs vaccinated as young as 3 weeks are protected all the way to market, he notes.

Serologic Kit Considerations Two commercial enzyme-linked immunosorbent assay (ELISA) kits now available for use in mycoplasma serologies are the Tween 20 and Dako ELISA. Tween 20 offers both good sensitivity and specificity, according to Gene Erickson, a diagnostician with the Rollins Veterinary Diagnostic Laboratory, Raleigh, NC. Dako ELISA is very specific for mycoplasma antigen, so sensitivity is lower.